1. Field of the Invention
This invention relates to a method for separating cells from a living cell-containing solution and more particularly, to a centrifugal separation method which eliminates damage to living cells and which provide cells free from contamination by bacteria.
2. Description of the Prior Art
Unlike bacterial cells, the propagation rate of animal cells is low and it is rather difficult to conduct continuous culture of a chermostat type. In order to culture industrially animal cells and to produce products, it is necessary to employ so-called "perfusion culture" which exchanges a liquid medium containing nutrient components with a waste liquor containing waste components while the cells are collected inside a culture tank. To keep the propagation of the cells by the perfusion culture, the cell separation must be repeated for a long period of time, such as at least one month, avoiding mechanical damage to the brittle cells under physiological conditions suitable for cells and a bacteria-free condition.
As described, for example, in "Hitachi Review", Vol. 4 (1987), p.p. 13-17, the manual separation operation has generally been employed in the past. In other words, a culture solution is charged in a centrifugal tube while paying the utmost caution so as not to cause bacterial contamination in a sterile chamber, then the cells are separated by an open type centrifugal apparatus. Then a supernatant is discarded, followed by suspending the deposited cells into a fresh medium and the cells are returned to the culture tank. This operation involves an extremely high risk of microbial contamination, and must be carried out by dividing the solution into small amounts. Since at least 1 or 2 hours is necessary for one batch, the cells are unavoidably placed, in the interim, under non-physiological conditions such as lack of dissolved oxygen, the drop of temperature, and the like.
Recently, a centrifugal apparatus of the sealed system type has been developed as disclosed, for example, in Japanese Patent Laid-Open No. 266151/1987 in order to separate blood and serum in hospitals. However, since the cell-containing solution comes into contact with a solid surface at a high speed and since a mechanical seal is employed while a rotary shaft penetrates through the outside, the brittle cells are likely to be damaged and there is the high risk of invasion of bacteria into the rotor chamber through the seal portion.